US and Russian warships took up positions in the Black Sea today in a risky war of nerves on opposing sides of the Georgia conflict.

With the Russians effectively controlling Georgia's main naval base of Poti, Moscow also dispatched the Moskva missile cruiser and two smaller craft on "peacekeeping" duties at the port of Sukhumi on the coast of Abkhazia, the breakaway region that the Kremlin recognised as independent yesterday.

The Americans, wary of escalating an already fraught situation, cancelled the scheduled docking in Poti of the US Coast Guard vessel, the Dallas, and instead sent it to the southern Georgian-controlled port of Batumi, 200km (124 miles) from the Russian ships, where it delivered humanitarian aid.

"Let's hope we don't see any direct confrontation," said Dmitri Peskov, the spokesman for the Russian prime minister, Vladimir Putin, as the Russians challenged the US policy of using military aircraft and ships to deliver relief supplies.

"The decision to deliver aid using Nato battleships is something that hardly can be explained," said Peskov. "It's not a common practice."

He said Russian naval forces were taking "some measures of precaution" around the Black Sea as the worsening dispute caused by Russia's recognition of Abkhazia and South Ossetia independence brought strong criticism from the key European countries most reluctant to sever relations with Russia.

The German chancellor, Angela Merkel, spoke to President Dmitri Medvedev today, the first western leader to talk to the Kremlin since Medvedev announced the recognition of the two secessionist regions of Georgia. She made it plain she had voiced her strong disapproval to the Russian leader.

"I made clear above all that I would have expected that we would talk about these questions in [international] organisations before unilateral recognition happened," she said. "There are several UN Security Council resolutions in which the territorial integrity of Georgia was stressed, which Russia also worked on."

The French foreign minister, Bernard Kouchner, said Russia had broken international law and, along with other senior European officials, worried that Russia's decision to redraw Georgia's borders would encourage Moscow to act similarly with other former parts of the Soviet Union such as Ukraine.

"We cannot accept these violations of international law ... of a territory by the army of a neighboring country," he said.

Germany and France, who opposed the US and Britain in April in blocking Georgian negotiations to join Nato, have been the most reluctant to punish Russia for the Georgian conflict of the past three weeks and are desperate to try to revive the Russia-Georgia peace plan mediated by the French president, Nicolas Sarkozy, a fortnight ago.

Paris and Berlin agree the unilateral recognition of Abkhazia and South Ossetia by Russia left the peace plan ineffectual. A summit of EU leaders in Brussels on Monday is to ponder Europe's options.

With mounting warnings of western economic or trade sanctions against Russia, an EU official admitted that threats to block Russian membership of the World Trade Organisation (WTO) were meaningless. The push for Russian admission being driven not by Moscow but by western business interests keen to tap the large Russian market, he said.

Peskov warned that trade sanctions against Moscow would hurt the west as much as Russia.

He admitted that South Ossetia, a mountainous region of 70,000 people, would struggle to establish itself as an independent state, but stressed that Russia's constitution made it possible for Russia to expand.

"My country will extend the arm of cooperation and friendship to ease the transition period [for South Ossetia]," he said.

EU officials complained that Moscow was seeking to control the distribution of international relief. EU aid officials were demanding entry to the Russian controlled regions, but were being barred unless they handed over the aid to the Russian authorities for distribution.